Journal of the NACAA
ISSN 2158-9429
Volume 3, Issue 2 - December, 2010

Replicated Asparagus Cultivar Evaluation 2007-2010

As more people are moving into North Carolina from northern states, where asparagus is commonly grown, they look to buy it from local growers here. It is a high-value horticultural crop that is easy to grow and can bring in extra income for growers.

 

For over 25 years, many new asparagus cultivars are being released as male hybrids. Asparagus is normally dioecious, having male and female reproductive structures (flowers) on separate plants. Female plants expend energy to produce seed while in the fern growth stage. Because of this, female plants yield 50-75% less spears than male plants, which produce no seed (5). Seeds from female plants fall to the ground and germinate, causing a seedling asparagus weed problem. For this reason, asparagus breeders in the U.S. and other countries have gone with male hybrids obtained from super male parent plants. The late Dr. Howard Ellison, former asparagus breeder at Rutgers University, observed that although asparagus produces both male and female plants, about one in 500 male plants would produce male flowers and a few flowers with functional male and female parts. By selfing flowers on one of these plants, called “hermaphrodites,” Ellison produced his first super male hybrid. When these super males are crossed with a female, the F₁ generation is all male, with no seeds produced. These super male hybrids yield about two to three times the amount of the older dioecious open-pollinated varieties, such as Mary Washington (4).

 

Spear tenderness is determined by the tightness of the spear tip, not by spear diameter. A tight spear tip will cause the spear to be tender while a loose tip will cause the spear to be tough and fibrous. As the spear tip opens up or “ferns out”, fiber development starts in the base of the spear to enable the elongated spear to change into a woody stalk to support the weight of the fern. As temperatures increase over 70 degrees F., spears will fern out at shorter heights, causing the grower to pick shorter spears (sacrificing spear height) in order to harvest tender spears of high quality. Under these conditions, a grower will need to pick at least once a day. Under cool temperatures below 70 degrees, spears will elongate more before ferning out, enabling the grower to harvest taller spears with tight tips that remain tender, with the grower picking once every 2-3 days (3).

 

 

In this trial, the following asparagus cultivars were grown:

Jersey Giant, Jersey Supreme, Jersey Gem, Jersey Knight and Jersey King are super male hybrids released from Rutgers University by the work of Drs. Howard Ellison and Stephen Garrison. They were the early pioneers in the discovery of male hybrid asparagus. Jersey Giant is a cross between NJ 56 (female) and NJ 22-8 (super male). Jersey Supreme is a cross between NJ 44P (female) and NJ 22-8 (super male). Jersey Gem is a cross between NJ G27 (female) and NJ 22-8 (super male). Jersey Knight is a cross between NJ 277C (female) and NJ 22-8 (super male). Jersey King is a cross between MD 10 (female) and NJ 22-8 (super male).

 

The UC (University of California) 157 cultivar is the progeny of a single cross between a male plant (not a super male) M 120, and a female plant, F 109. Frank Takatori and Frank Southers at the University of California at Riverside developed UC 157 in 1978. 

 

UC 115 (DePaoli) is an asparagus hybrid that is produced by a cross between the female parent clone F600 and the male parent clone M256. The name DePaoli was selected to honor Mr. William DePaoli, Manager of the California Asparagus Commission from its creation in 1990 until his death in 1999.  De Paoli is a dioecious hybrid, and is similar to UC 157 in spear size.

 

Newer California hybrids include Atlas, Apollo, and Grande that were released by Dr. Brian Benson of California Asparagus Seed and Transplants, Inc. These cultivars all have the female parent of the UC 157 cultivar and a male parent from the Rutgers University asparagus breeding program. These hybrids are dioecious with female plants producing seed. 

 

Purple Passion is a selection from Violeta d’ Albinga(cultivar from Albinga, Italy). It is an open-pollinated cultivar with many seeds produced from the female plants. Spear yield is lower than other varieties but spear diameter is very large. It has a burgundy color and is sweeter than green asparagus. When cooked, the purple pigment is destroyed and reverts back to green.

 

Dulce Verde is a cultivar that is higher in sugar content than other green asparagus cultivars. The fern growth on this cultivar was considerably stunted, compared to other cultivars during the 2007 harvest season. Brian Benson (see above) decided to discontinue this variety in 2007 and its poor yield caused it to be removed from my trial at the end of 2007.

 

Guelph Millennium is a recent male hybrid cultivar release from the University of Guelph in Ontario, Canada by Dr. David Wolyn.

 

The attributes of the California Hybrids should enable the grower to harvest a taller spear (8-9 inches) at temperatures above 70 degrees F. without the tip of the spear opening up or “ferning out”, which causes spears to be tough.   Taller spears are heavier, having more weight per spear. The New Jersey male hybrids, University of Guleph Male Hybrid, and open-pollinated cultivars fern out at a shorter spear height (5-6 inches) under warm temperatures above 70 degrees F. (3).

 

The cultivars that were studied in this trial were chosen based on ones that are currently grown for commercial production that are standards in the industry, and ones that may show promise in the future.

 

 MATERIALS AND METHODS

 

Proper variety selection is important for grower success so a ¼ acre replicated asparagus cultivar trial was planted at the Garnett Carr farm in Roxboro, NC with 13 cultivars. Seeds were sown in the greenhouses of Aarons Creek Greenhouses in Buffalo Junction, VA on January 20, 2005, and 15-week-old seedling transplants were planted into the field on May 4, 2005 in an Appling Sandy Loam soil. A randomized complete block design with 12 plants per plot and 4 replications was used. Transplants were spaced one foot between plants in the row and five feet between rows and planted in the bottom of a 6 inch deep furrow as recommended by Cantaluppi and Motes (2,3,6).  As new spears emerged, and as new ferns were formed, the furrows were filled in below the lowest fern branchlets until the furrows were completely filled in at ground level.  Since the trial was planted using seedling transplants, no harvest was taken in 2006. This was done to build food reserves in the crown of the plant to strengthen the plant for a 2-week harvest in 2007. 

 

The transplants were irrigated as needed during the first growing season only. Irrigation is normally not needed during field establishment and beyond if establishing a field from crowns (roots) from one-year-old plants in areas where the rainfall is 30 inches or more per year (3). However, irrigation is imperative during the establishment year with seedling transplants, since they do not have a one-year-old established root system that can tolerate periods of drought. Irrigation is needed in areas where less than 30 inches of rainfall occur per year. Seeds were used to establish this trial because most of the cultivars were not available as crowns.

 

The trial was harvested for two weeks in 2007, four weeks in 2008, six weeks in 2009, and eight weeks in 2010, and will be for eight weeks thereafter for each succeeding year. This harvesting frequency was chosen following research recommendations made by Benson and Motes (1), Motes (6), and Cantaluppi (2) which showed that harvesting asparagus that was established by planting one-year-old crowns, one year after planting (the second year), caused no reduction in subsequent yield, but provided the grower with an income one year earlier than did harvesting two years after planting.  Also, in the second year after planting (the third year), the average spear weight was found to be significantly greater in plants that were harvested the previous year than in plants not harvested the previous year.  The increase in spear production may be due to the release of buds from supression by older shoots (1,2,6).

 

Asparagus spears can be cut or snapped to produce spears of marketable length, which is usually between 7 and 9 inches, depending on tip tightness. Asparagus spears may be cut below the soil surface with a knife, or they may be hand-snapped above the soil surface. Cutting asparagus requires more labor, but increases yield 20 to 25% because spears are longer. However, cutting spears below the soil greatly increases the chance of the knife injuring a bud or an emerging spear on the same crown (3).

 

When hand-snapping, the spear usually breaks above the area containing fiber. In other words, the portion of the spear left in the field will be fibrous, while the harvested spear is tender and is completely edible. The small stub left above the soil after snapping dries up and disintegrates. A new spear does not come up at that spot, but comes up from another bud that enlarges on another part of the crown. Snapped asparagus has no trim-off waste and should command a higher price than cut asparagus with white butts (3). In this trial, it was decided to snap spears instead of cutting because of the above reasons and is the preferred and accepted method by most growers.

 

 RESULTS

 

Yield data was recorded in lbs./acre. This was obtained by dividing the total square feet of one plot row (60), into 43,560 (the number of square feet in one acre) to get 726-60 square foot rows in one acre. Data that was recorded included total yield per cultivar, the yield (and percentage) of spears per cultivar that were greater than 3/8ths inch in diameter, the yield of spears that were less than 3/8ths inch in diameter, and the number of spears per plant that each cultivar produced. Recording yield data in terms of spear diameter (an industry standard), also allows the grower to select a cultivar that would be suitable to him and his customers’ preferences. Recording the number of spears produced per plant per cultivar lets the grower compare spear output per cultivar over time. The harvesting frequency was based on how fast the spears grew, based on air temperatures as previously described, resulting in harvested spears that had tight tips, before they started to fern out.

 

 

 

 

Harvest started on March 15, 2007, with just a few spears each of Grande, UC 157 and UC 115. A frost occurred on March 19 which delayed future spear emergence until March 26. The other cultivars then started to emerge with the exception of Purple Passion, Dulce Verde, and Guelph Millennium, which did not emerge until April 2.

 

The last harvest was taken on April 5 because on April 6, 7, and 8, severe frosts occurred. A decision was made to end the 2007 harvest at this time, as the harvest period lasted three weeks, with an actual harvest of two weeks for most cultivars, with one week being lost to frost. A total of 10 harvests were made. Guelph Millennium was one of the latest ones to emerge before the second frost occurrence in 2007, and it did not get a chance to fully perform before the harvest was terminated, hence the low yields.

 

 Observations of the 2008 Trial

The drought of 2007 seemed to have no impact on asparagus yields in 2008. When people viewed the trial plots on August 17, 2007, 40 people braved the 104-degree heat to see asparagus ferns standing like a green oasis, which received no water all year, growing in an Appling Sandy Loam soil. This is a great testament for the extreme drought tolerance of asparagus.

 

In 2008, harvest started on March 22 for most cultivars with the exception of Guelph Millennium. Cool temperatures occurred below 70 degrees until April 11, when yields accelerated, and Guelph Millennium started to emerge. One frost in mid-April set yields back for one week. Then yields increased until it was decided to end the harvest on April 26. The harvest period lasted five weeks, with an actual harvest of four weeks for most cultivars, with a one-week slump in yield, due to frost. A total of 21 harvests were made.

 

 Observations of the 2009 Trial

The 2009 harvest went smoothly, with only one light frost on April 6 that brought temperatures down to 31-32 degrees, without a harvest delay after the frost. Harvest started on March 24, with Guelph Millennium (GM) not showing the 20-day delay in emergence compared to other cultivars as it showed in 2008. Instead, two out of four GM treatments had spears emerging on March 24, with the other two treatments starting four and ten days later, respectively.

 

The majority of days were cool, with temperatures rarely getting over 85 degrees. So there were no “growth flushes” that would cause a large number of spears to be produced in a short period of time. The harvest period lasted six weeks with a total of 36 harvests.

 

Harvest started on March 26, with one frost on March 28 that brought temperatures down to 30 degrees and delayed the next harvest for five days. There were no other frosts during the season. Two Guelph Millennium (GM) treatments had spears emerging on March 26, and the other two treatments had spears emerging seven days later.

 

There were a few days of cool temperatures, but most were above 70 degrees with very little rainfall. This made the number of “growth flushes” minimal. The harvest period lasted eight weeks with a total of 41 harvests.

 

 SUMMARY

 

 

This table shows how each asparagus cultivar ranked in numerical order from highest yielding (1) to lowest yielding (12) in 2007, 2008, 2009, and 2010.

 

 

Table 5 shows the cultivars having yield stability during the last four years are Jersey Giant, and Jersey Supreme. Jersey Giant still yields well and has a wide geographic adaptability across the U.S.

 

Yields of some of the California hybrids have decreased, while others have moved up and down. More time is needed to properly evaluate these cultivars. Purple Passion yields have remained fairly stable. Yields are low but growers should be able to get higher prices because of its purple color and higher sugar content than green asparagus.

 

Guelph Millennium yields have steadily increased each year from 12^th place to 1^st place in four years, however, spears greater than 3/8” in diameter are averaging about 50%, compared to the other cultivars which are between 70-90% which should not be of great concern to growers if their customers will buy smaller diameter spears. It will be interesting to see if it will remain a high-yielding cultivar.

 

In a virgin soil (free of Fusarium), the expected productive life of an asparagus field (any cultivar) is 15-20 years. Growers feel that peak production occurs in the 6^th or 7^th year, with the best production occurring during years 7-12. There is a decline of production of about 5% per year in the 10^th year and every year thereafter. After the 15^th year, the field may no longer be economically profitable. Established asparagus growers recover their investment after the 5^th year and years 5-10 are their most profitable years (7).

 

Data collection in this trial will be on-going for at least another 8 years to evaluate the longevity of these cultivars. During this time, total yields between cultivars can be compared by getting a more realistic picture of how they perform over a period of 12 years.

 

 

1.     Benson, B.L., and J.E. Motes. 1982. Influence of harvesting asparagus the year following planting on subsequent spear yield and quality. HortScience 17(5): 744-745.

 

2.     Cantaluppi, C.J. 1990. Back to the basics-getting started in asparagus production, pp. 1-18. In: C. Cantaluppi (ed.). Proc. 1990 Illinois Asparagus School Hort. Ser. 85. Coop. Ext. Serv. Univ. of Illinois at Urbana-Champaign.

 

3.     Cantaluppi, C.J. and R.J. Precheur. 1997. Asparagus production, management, and marketing, Bulletin 826, The Ohio State University Extension, Columbus, OH.

 

4.     Garrison, S.A. 1991. New hybrid asparagus varieties for the Midwest, pp. 13-21. In: C. Cantaluppi (ed.). Proc. 1991 Illinois Asparagus School Hort. Ser. 89. Coop. Ext. Serv. Univ. of Illinois at Urbana-Champaign.

 

5.   Hexamer, F.M. 1909. Asparagus--Its culture for home use and for market. Orange Judd Company, NY pp. 40-42.

 

6.     Motes, J. et. al. 1994. Asparagus production. OSU Extension Facts F-6018. Oklahoma Coop. Ext. Serv., Stillwater, OK.

 

7.     Walsworth, R. 1995. Personal communication. 48^th Ave., Rt. 1, Mears, MI 49436.